5.12.3 Defining Symbols ¶

You can use the ‘def’ directive to define or redefine a symbol:

name    def     value

This statement defines or redefines a symbol name to a value. A symbol name must start at the beginning of a line. A symbol value must not contain commas outside of string literals.

There are two possible scopes of a symbol: global and local. Defining a symbol outside of macros makes the symbol global. If a symbol is global one, a ‘def’ directive used for the symbol inside a macro redefines the global symbol to a new value.

Defining a symbol inside a macro makes the symbol local. Macro arguments are also local symbols. Local symbols are not visible outside of macros containing their definitions. If a symbol is local one, a ‘def’ directive used for the symbol inside a macro (containing the symbol definition) redefines the local symbol to a new value.

QSMM 1.19 introduces the ‘ldef’ directive for using inside a macro:

name    ldef    value

This statement defines or redefines a local symbol name to a value even if there exists a global symbol name.

Use the ‘def’ directive for defining or redefining global symbols and use the ‘ldef’ directive for defining or redefining local symbols.

The assembler preprocessor replaces with a symbol value every occurrence of a symbol name as a token in a symbol scope. To concatenate a symbol value with adjacent tokens, prepend and/or append the characters ‘##’ to a symbol name token.

For example, the source text

st      def     01

        choice
        case    a##st##_00, l##st##_00
        case    a##st##_01, l##st##_01
        end     choice

        jmp     l##st##_02

preprocesses to the text

        choice
        case    a01_00, l01_00
        case    a01_01, l01_01
        end     choice

        jmp     l01_02

If a symbol value is not a (quoted) string literal, prepend the character ‘#’ to the symbol name token to convert the symbol value to a string literal. For example, the source text

id       def     5

s##id:   stt     #id

preprocesses to the text

s5:   stt     "5"

The right-hand side of a symbol definition or redefinition can contain symbol names. After expanding the symbol names, the value of the symbol must reduce to either a string literal or other text without string literals, spaces, and commas.

The assembler preprocessor supports the predefined symbol ‘__UNIQUE__’ expanded to the next number from the sequence of natural numbers. You can use that symbol to generate unique location labels in macros.